1. Field of the Invention
The present invention relates to methods and apparatus for use in a distribution cabinet of an optical communication system, and more specifically to distribution apparatus which allows the addition on demand of substantially a maximum number of electrical RF (radio frequency) user channels onto a wavelength carrier at a specific wavelength before being required to add another optical transmitter for generating a carrier at a different wavelength. That is, the addition of an optical generator for generating a specific wavelength may be substantially delayed until the optical wavelength carrier in use is almost to saturation. This is done without substantial downtime by making simple terminal connections between the existing panels.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
The communications industry is using more and more optical or light fibers in lieu of copper wire. Optical fibers have an extremely high bandwidth thereby allowing significantly more information than can be carried by a copper wire transmission line such as twisted pairs or coaxial cable. However, because of the different usage of cable modem transmissions in various neighborhoods (commonly referred to as penetration), there may be some areas either business or residential where the penetration is almost one hundred percent. That is, almost every household path (HHP) will require the use of a cable modem transmission whereas other neighborhoods may be at substantially zero penetration.
However, just because an area may be at zero penetration at one point in time suggests that the growth rate in that area may be very rapid, and a need exists so that such rapid grown can be handled quickly and inexpensively without the major addition of new equipment and without significant downtime to the customer.
The above objects and advantages are achieved in the present invention by distribution apparatus in an optical communication system which allows the addition on demand of substantially a maximum number of cable modem transmission user channels with minimum downtime and at no expense. In areas of low usage or low penetration, an optical fiber may carry a single wavelength of light which is modulated by RF signals around a center wavelength of light of about 1550 nanometers. The same optical fiber carrying the 1550 nanometers of light will typically also be capable of carrying other wavelengths of lights which have center wavelengths close to the 1550 nanometers but somewhat displaced so as to have good isolation between the signals. For example, if it were desirable to carry three different wavelengths of light, the center frequencies might be selected to be 1545 nanometers, 1550 nanometers, and 1555 nanometers. The use of three different wavelengths of light as discussed will provide ample separation such that there is no cross talk or interference between the different wavelengths of light. In fact, up to eight different and specific wavelengths of light may be selected around the base wavelength referred to as 1550. Each of these different eight wavelengths may be referred to as xcex such as xcex1, xcex2, xcex3, xcex4, xcex5, xcex6, xcex7, and xcex8. The 1550 nanometers of light which is considered a base wavelength is selected to minimize the transmission loss of the optical fibers. Certain ones of the most used optical fibers will typically have transmission characteristics such that certain wavelengths are highly desirable as center wavelengths such as, for example, 1550 nanometers, 1310 nanometers, and 960 nanometers of light. However, to understand how eight different wavelengths of light around the 1550 nanometer length can exist at the same time may best be understood by thinking of the 1550 nanometers being one of the best possible wavelengths for transmission over the optical fiber, yet 1545 and 1555 nanometers also are very efficient transmissions. Therefore, so long as there is sufficient separation between the various wavelengths of light such that there is no cross talk or interference from each of the various wavelength transmissions, there is sufficient bandwidth to readily handle a large number of customers such as, for example, 768 cable modem customers. The novel apparatus of this invention which allows such flexibility, comprises a first group of combining circuits each of which has a plurality of inputs and a single output. Each of the combining circuit inputs is capable of receiving an input signal on each one of the plurality of input terminals. The plurality of input signals which may be of different frequencies are then directly combined by the combining circuits and provided as an output signal made up of these combined received input signals on the single output terminal. In a preferred embodiment, the plurality of inputs and the single output terminate in an SMB-type coax connector. Further, each one of the inputs may itself be carrying signals from up to at least 24 HHP""s (household paths) or cable modem customers. The inputs to the input terminals are provided by a multiplicity of input cables each of which may be carrying, as mentioned above, up to at least 24 different channels or signals from 16 different cable modem customers. Each one of the input cables will also terminate with an SMB connector suitable for mating with the SMB connectors on the first group of combining circuits. There is also a second group of combining circuits similar to the first group in that they also have a plurality of inputs and a single output. Each one of the second group of combining circuits receives one of the outputs from one of the first group of combining circuits and then, as in the same manner as with respect to the first group of combining circuits, combines these inputs to produce a combined output signal which is made up of all of the output signals received from the first group of combining circuits. The inputs of this second group of combining circuits is also a first type of connector, such as an SMB connector as discussed above.
Then, depending upon the level of penetration, the output of the second group of combining circuits may go directly to an optical transmitter which generates light over a frequency band at a very select center wavelength around 1550 nanometers of light. Alternately, the output from the second group of combining circuits goes to a third or final combining circuit. The final combining circuit, in the same manner as the first and second groups of combining circuits, receives the output from the second group of combining circuits as input signals and combines these signals into a final or modulation output signal which is used to modulate the wavelength of light generated by the optical transmitter.